1. Field of the Invention
This invention relates to circulation controlled rotorcraft, and in particular, to a rotorcraft having a fluid dynamic control surface with a blowing slot and a means for controlling the rate and volume of fluid through the blowing slot.
2. Related Art
It is a well known aviation principal that increasing the lift capability and/or lift distribution of an aircraft""s wings results in the aircraft being able to handle heavier payloads. As a result, aircraft wings have been the focus of redesign efforts in order to increase their lift capabilities. The goal of this research was to increase take-off weight limits or provide the aircraft with flight and control characteristics suitable for a greater range of environmental or mission related flight requirements.
Recent research developments have incorporated blowing slots upstream of a rounded trailing edge of an aircraft""s wings to provide increased lift and/or control of the aircraft. It has been shown that a jet of air exiting at the proper location on a lifting surface, e.g., a wing, either increases the effective wing area and helps minimize the boundary layer separation near the trailing edge of the wing, thereby increasing lift, or increases the lift force by Coanda turning along the rounded trailing edge.
While this research effort enhanced the lift capability of fixed wing aircraft, it fell short of providing the same advantages for rotorcraft, e.g., helicopters, for several reasons. The inboard portion of the rotor blades (wings) of a conventional rotorcraft in flight experience a period of reverse flow during part of the cycle. Therefore, by adding an extra blowing slot along the inboard section of the rotor blade, the rotor blade""s leading edge can be reversed as needed to provide lift over the entire length of the rotor blade, that is, to increase lift during an entire rotation of a rotor blade.
To accomplish this increase in lift of a rotor blade, an elaborate and complex air handling valving system was incorporated into the rotor hub mechanism of a rotorcraft. Positioning the air valves in the rotor hub mechanism resulted in greatly increased drag and power waste during the period of filling and emptying the rotor blade with compressed air.
It was found that subsonic blowing velocities were needed over most of the entire length of a rotor blade; that it was nearly impossible to effectively distribute the compressible air over the entire length of the rotor blade; that an uninterrupted uniform blowing slot was needed; that to control the blowing rate during an entire revolution of a rotor blade, either the blowing pressure or the blowing slot width must be dynamically controllable to achieve the needed balance of lifting moment about the rotor hub. In addition, all attempts of controlling the blowing velocities along the entire length of a blowing slot included the use of a mechanical camxe2x80x94and all failed.
To balance the lifting moment, the blowing slot flowing pressure must be dynamically controlled. This was found to be a very power wasting procedure because the air was supplied intermittently to the rotor blade, so that the average pressure is only half the supply pressure. To achieve this dynamic control, a rotor hub was designed having a large number of control valves around its perimeter to regulate the amount of blowing air to the front and rear compartments of a rotor blade during its rotation. The volume of the rotor blade compartments acted as large capacitors. Therefore, at a high frequency of rotation, the blowing slot""s outflow rate becomes continuous and only somewhat modulated even when the air supplied by the valves is intermittent. In addition, all attempts to control the flow of air at the rotor hub failed because air is a compressible fluid and, as such, the fluid control needs to occur along the entire length of the blowing slot and not at the rotor hub. Therefore, adequate control of the air pressure along the length of the blowing slot of the rotating rotor blades was never achieved.
Therefore, there is a need for a fluid, e.g., air, handling and control system for a rotorcraft that controls a rotor blade""s leading edge and trailing edge as needed to provide lift over the entire length of the trailing edge, thereby providing the correct amount of lift during an entire rotation of the rotor blade. There is a further need for a fluid handling and control system for a rotorcraft that provides dynamic control of the pressure of a fluid, e.g., air, through a blowing slot along the entire length of a blowing slot in the rotor blade to avoid operating the blowing slot at only half the air supply pressure.
The present invention solves the problems associated with the use of a blowing slot in a dynamic fluid control surface, e.g., a rotor blade, of a rotorcraft having the control valves that provide the circulation control positioned upstream of the rounded trailing edge. The present invention is a dynamic fluid control surface having a blowing slot along the length of a trailing edge and one or more piezoelectric actuators positioned along the length of the blowing slot to open and close the blowing slot as needed. The piezoelectric actuators are controlled by a computer system such that they are engaged and disengaged as needed during the rotation of the dynamic fluid control surface.
There are many advantages with positioning the piezoelectric actuators along the length of a blowing slot of a dynamic fluid control surface. First, the scope of the present invention may be incorporated into a dynamic fluid control surface, i.e., rotor blade, of a rotorcraft as well as with any vehicle having a dynamic fluid control surface, including fixed wing aircraft, watercraft, or others.
Other specific examples of such advantages are described in terms of a rotorcraft, e.g., a helicopter, incorporating the present invention: The rotor lift capability is enhanced. If sufficient rotor blade torque is provided by the blowing slot then the need for a tail rotor is eliminated. Loading symmetry and no rolling movements during a forward flight permits lower rotor blade tip speed ratios than conventional rotor blades. Less lift is required from a rotor blade in the reverse flow region. The rotorcraft may be steered (forwards, sideways, up, and down) by varying the piezoelectric actuators"" gaps and opening times along the length of the blowing slot of the rotor blade, thereby eliminating the complex mechanical control system in conventional helicopters. Icing problems along a rotorblade are eliminated as the blowing fluid, e.g., exhaust air, from a gas-turbine compressor bleed is sufficient to warm and de-ice the rotor blades. The simple see-saw suspension of the rotor blades assures zero roll moment about the rotor hub. A stored gas, e.g., hydrogen peroxide plus a catalist, within the rotorcraft can provide sufficient working fluid for an emergency landing such as in case of an engine failure.